Previous studies in this laboratory have shown that cats can be infected with Brugia malayi in such a manner that developing and adult worms remain localized in lymphatics of the hind leg. This facilitates studying the effect which developing, mature and dying worms have on the function of the popliteal lymph node and its afferent vessels. It also provides an opportunity to study the effect which concurrent secondary infection with microorganisms has on this drainage system. This should help to clarify the role which secondary infections may play in progressive tissue damage which ultimately leads to "elephantiasis" in a proportion of filariasis patients who suffer from repeated attacks of lymphadenitis and lymphangitis. Preliminary work showing that previous repeated infection of cats with Brugia malayi makes them significantly more susceptible to infection with a Group G Streptococcus of feline origin will be extended. Changes in susceptibility to bacteria will be assessed by observations on the production of fever, edema, skin lesions and culture of organisms from the affected limb. The acute as well as the chronic effect of combined Brugia and Streptococcus infection as compared to infection with either pathogen alone will be evaluated by lymphography, dissection following injection of lymph-staining dye, measurement of skin thickness, skin temperatures and production of lesions.